Gene Veith quotes his pastor:
“…It’s not primarily about what we do, it’s about faith. For to be a child as Jesus is describing here means to be dependent. To be dependent upon your Father in heaven, like a child, for everything – to supply your needs, to give you your identity, to rescue you, and to protect you from your enemies. It is to acknowledge that you are, in fact, utterly dependent and in need of Christ and His provision. It is to be weak and vulnerable, and to learn to see yourself in this way.
For no matter how strong or high or learned or powerful you may be in the world and in the eyes of the world, none of that matters when it comes to the kingdom of heaven. Here, greatness is quite different. Here, greatness is to be among those whom Christ serves. And to see others and to serve others in the same way. . . .”
Read it all here: http://www.geneveith.com/2011/09/07/the-greatest-in-the-kingdom-of-heaven